输出参数的Objective-C可为空性 [英] Objective-C nullability for output parameters

问题描述

我正在为类添加可空性说明符，并且我有一些指针到指针的输出参数，例如(NSString**)，因为该方法返回了多个对象.如何为此指定空性?

I'm adding nullability specifiers to a class, and I have some pointer-to-pointer output parameters, like (NSString**), because the method returns multiple objects. How do I specify nullability for that?

对于这些特殊情况，我希望调用者不要传递NULL，但是我不在乎他们是否传递指向nil变量的指针(或者，这是预期的).

For these particular cases, I want callers to not pass in NULL, but I don't care if they pass a pointer to a nil variable (or rather, that's expected).

起初我尝试了(nonnull NSString**)，在经过两轮Xcode的建议修复后，以(NSString* _Nonnull *)结尾，但是第二个*仍然警告:指针缺少可空性类型说明符"，没有建议修复.

At first I tried (nonnull NSString**), and after a couple of rounds of Xcode's suggested fixes, ended with (NSString* _Nonnull *), but there's still a warning on the second *, "Pointer is missing nullability type specifier", with no suggested fix.

推荐答案

您有两个指针，因此需要两个可空性说明符.

You have two pointers so you need two nullability specifiers.

- (void)someMethod:(NSString * _Nullable * _Nonnull)out

这意味着您必须传递非null指针，但可能会返回null结果.

This means you must pass in a non-null pointer but you may get back a null result.

这将失败:

[someObject someMethod:nil];

这将起作用:

NSString *result = nil;
[someObject someMethod:&result];

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